Storages and flows

Storages and flows

Big idea (learn this first): All systems have <strong>{{storages|A place where matter, energy, or information builds up over time. Also called a stock. Examples: water in a reservoir, CO₂ in the atmosphere.}}</strong>, <strong>{{flows|The movement of matter, energy, or information into or out of a storage. Flows change the amount stored.}}</strong>, and <strong>{{system boundaries|The imaginary line that separates a system from its surroundings. Everything inside is studied; everything outside is simplified or ignored.}}</strong>. If you can name these three, you can answer most IB questions.

[Diagram: storage-flow-basic] - Available in full study mode

What is a storage?

A <strong>{{storage|A place where matter, energy, or information builds up over time. Also called a stock. Examples: water in a reservoir, CO₂ in the atmosphere.}}</strong> (also called a <strong>stock</strong>) is a place where <strong>matter, energy, or information</strong> builds up over time.

<strong>Easy rule:</strong> if it can increase or decrease, it is a storage.

In system diagrams, storages are shown as <strong>boxes</strong> 📦. A bigger box means a larger amount stored.

What is a flow?

A <strong>{{flow|The movement of matter, energy, or information into or out of a storage. Flows change the amount stored.}}</strong> is the <strong>movement</strong> of matter, energy, or information <strong>into or out of</strong> a storage.

<strong>Flows change storages.</strong> No flow = no change.

In diagrams, flows are shown as <strong>arrows</strong> →. A thicker arrow means a larger flow.

See it in action: Reservoir example

[Diagram: reservoir-system] - Available in full study mode

⚠️ Inputs vs inflows (IB exam trap!)

Students often mix these up. Here's the simple difference:

In exams, say **"rainfall is an inflow"**, not **"rainfall is an input"**. The water itself is the input; rainfall is the process (inflow).

System boundaries

A **{{system boundary|The imaginary line that separates a system from its surroundings. Everything inside is studied; everything outside is simplified or ignored.}}** shows what is included in the system and what is left out.

Good models choose a **useful** boundary, not a perfect one. There is no single "correct" boundary.

The 5 key rules (VERY exam-important)

[Diagram: equilibrium-diagram] - Available in full study mode

Real-world example: The carbon cycle

Let's apply storages and flows to something you'll see in exams:

Transfers and Transformations

**Flows** move matter or energy through a system. There are two main types you need to know for the IB.

Transfers

A **{{transfer|The movement of matter or energy from one place to another without changing its form.}}** happens when something moves location but stays the same.

**Key idea:** Same substance, new location.

Transformations

A **{{transformation|A change in the form, state, or chemical nature of matter or energy.}}** happens when something changes into something different.

**Key idea:** Something new is created.

Memorise

In any "explain using systems" question, identify: